jdfromaz

04 ES 330

When car is cold I fill the coolant reservoir just above the minimum "L". I open the hood and run the engine idle for about 5-10 minutes. Coolant starts leaking out the "vent hole" on the cap (the opposite side of where the tube from the radiator cap is attached). So in the morning the reservoir is empty, I fill it above L, drive a bit, and there's a puddle under the reservoir tank area.

In the photo, if I run the engine, coolant will leak out the tube shown in the left side of the cap. So far engine has not overheated - I keep adding coolant.

The radiator cap, thermostat, radiator, and two hoses are under 90 days old. I took it in and the mechanic said all that was wrong was a leak in the tube from the radiator cap to the overflow tank. He replaced it with a new hose. The overflow cap is old but it looks so simple that I can't imagine it being broken so long as the tubes (inner and outer) connect property, and they do.

Am I missing something obvious?

coolant reservoir filled to L. Coolant leaks out the left side of the cap when engine reaches operating temperature. m

Arsenii

Hello,

Was the issue present with old OEM parts?

My first suspect would be the cap that won't hold pressure. The thing is that Radiator Cap is not there just to seal the system, it has a Bypass Valve built into it, which regulates the pressure in the system, allowing excess to drain into the Expansion Tank. Because of that, I would Only trust OEM part with the Cap and the Thermostat, straight from the dealership and not eBay or Amazon, if yours is not an OEM part, I would start with that regardless of whether it is the cause or not.

Hope this helps and best of luck!

jdfromaz

Thanks. Another radiator cap was the next thing I was going to try, despite it being brand new.

My understanding of the system is only partial, but it seems from my reading that the purpose of the reservoir is that when the engine gets hot, coolant expands, and the radiator cap opens from the pressure and coolant flows into the overflow tank where it gets sucked back in when the engine cools.I thought the vent hole in the reservoir cap was only for when the overflow tank overflowed. (note to readers: in this car the reservoir is not pressurized like I understand that some others are)

So if that's close to right, I'm confused to why with a nearly empty reservoir, coolant would come into one side of the cap and go out the other side rather than going into the tank where there's plenty room (even if the radiator cap was opening prematurely??)

The reservoir cap is old and I plan to replace that also asap, when I can get the part but it's not clogged or blocked.

LeX2K

The reservoir cap allows air to be pushed out/sucked back in. You understand the system correctly the rad cap controls coolant flow to the reservoir based on temperature. Did you use a Toyota radiator cap?

You sure the reservoir cap isn't backwards? I think there is a check valve in it.

jdfromaz

The radiator cap is under 6 months old but I don't know if it was genuine toyota. I had it replaced by my usual independent shop. After a radiator leak and overheat incident this summer i had the radiator, radiator cap, thermostat, hoses replaced and engine tested for damage (which was ok). I took it back for this leak and they did diagnostics on the system and said it was fine other than a leak in the tube from the cap to the reservoir cap which they replaced, but coolant still leaks from the reservoir cap and I don't know if it's worth going back to them again if I can avoid it.

LeX2K

Has to be genuine Toyota no exceptions.

fortitude

I think you are absoulety correct. Here is a picture of mine. Notice the writing "coolant" on top and the tube connected to the right side

OP looks reversed

jdfromaz

Yes! The hose was connected to the wrong side.
Thanks for the photo.

LeX2K

Did it fix your problem?

jdfromaz

The shop had replaced that small hose and put a new one on the wrong side of the overflow tank cap, leading to the issue.

So when coolant was forced out of the system and into the tank (through the vent hole), it pushed up the inside tube and out the inlet hole, resulting in a puddle under that area. I only drove a few miles like that and did not experience any signs of overheating, just the puddle wherever I went and the near-empty tank. When the car cooled down it must have sucked air into the system rather than coolant.

Today I topped off the radiator through the radiator cap hole. I was about a quart low. Then I filled the overflow tank halfway between L and H. After a couple test drives, it all seems ok now.

Since the problem caused the radiator to get low, I read about bleeding it. Lots of mixed information. Some say run with the radiator cap off, then top off when it cools down. Some say buy a special kit with a sealing funnel, and others say never do it yourself. I decided to leave it alone and watch for signs of air in the system (according to a list I read).

LeX2K

You don't need to do anything a few drive cycles will purge any air.